1. Technical Field
The present invention relates generally to vehicle occupant protection. More particularly, the present invention relates to an intrusion beam for a vehicle door and a method for making the same.
2. Discussion
Conventional vehicle doors typically are equipped with a rigid intrusion beam structure to protect vehicle occupants from injuries resultant from a side impact. This practice has generally proven successful in meeting current side impact Federal Motor Vehicle Safety Standards (FMVSS) which require a static test. In the current test, which is technically a quasi-static test, a ram is slowly forced into the side of a stationary vehicle. The vehicle door is required to meet minimum specified force-deflection characteristics. There are three requirements of the current test--initial crush, intermediate crush and peak crush. The peak crush is a minimum specified load requirement that must be achieved during the first 18 inches that the ram is advanced into the side of the vehicle.
Extensive testing done with an anthropomorphic test device (ATD), otherwise known as a crash dummy, has indicated that the current standard is not entirely representative of actual side impact collisions, and further that compliance with the current standard is not necessarily sufficient to protect vehicle occupants. During a vehicle side impact collision, as with most dynamic collisions involving one object substantially stationary with respect to the direction of impact, two impacts actually occur. When a first car, the striking car, collides with a second car, the struck car, a first impact occurs immediately. Milliseconds later, the second impact occurs in which the occupant and the interior of the vehicle door collide. Importantly, it is this second impact which directly inflicts injury upon the vehicle occupant.
As a result of the current standards' inability to sufficiently replicate the results of a vehicle side impact collision, an amendment to the side impact standards (FMVSS 214), adopted Nov. 2, 1990, requires a dynamic test. In this test, a moving barrier, simulating a striking vehicle, impacts a stationary vehicle at a speed of 33.5 miles per hour. Thoratic and pelvic accelerations taken from the ATD are monitored. The accelerations are then compared with specified maximums provided by the amended standard. The FMVSS dynamic requirements will be in addition to the static, or quasi-static, requirements of the current standard. Dynamic standards are scheduled to be gradually implemented begin in 1994.
The applicability of the two tests is listed immediately below.
______________________________________ VEHICLE TYPE STATIC DYNAMIC ______________________________________ PASSENGER CARS CURRENT 10% 09-01-1993 25% 09-01-1994 40% 09-01-1995 100% 09-01-1996 LIGHT TRUCKS 90% 09-01-1993 NOT CURRENTLY 100% 09-01-1994 PLANNED ______________________________________
With the retention of the current test, coupled with the pending adoption of the dynamic test, it is critical that intrusion beam structures be designed so that a vehicle door is capable of meeting both standards. It is recognized by those skilled in the art that dynamic test results can be greatly improved through the addition of padding and minor structural changes to the belt-line region of the door. Accordingly, a need exists for intrusion beam designs which meet static requirements while also permitting sufficient space for such padding and structural changes necessary to improve dynamic test results.
Historically the most difficult portion of the static test is the initial crush requirement. During the test the loading ram is placed in contact with the outer panel which may be located 1/2 inch or more from the intrusion beam. The load does not increase appreciably until the ram contacts the intrusion beam. Therefore, the initial stiffness of the door beam is critical.
The stiffness of an intrusion beam structure is controlled by the modulus of elasticity of the material and the moment of inertia of the beam cross section. The moment of inertia is dependent on section geometry. The most efficient way to increase the moment of inertia is to increase cross-sectional depth. However, the cross-sectional depth is limited by internal door packaging requirements and component weight restrictions. Increasing the section depth also results in higher beam stresses for a given displacement. This leads to an early yield point in the load vs. displacement curve, and is potentially detrimental to an intrusion beam's performance.
Heretofore, many intrusion beams having the practical cross-sections capable of meeting the initial stiffness requirement of the static test result in yield or collapse after only a few inches of ram penetration. During the static test, after the initial crush, an intrusion beam makes a transition from that of a bending member to a tensile member. In the tensile mode, significantly large tensile loads are transferred to the ends of the intrusion beam.
Several devices used to reinforce vehicle doors from the impact of a side collision are known. U.S. Pat. No. 3,868,141 to Johnson relates to elongated members disposed vertically between the exterior panels of a vehicle door. U.S. Pat. No. 3,700,076 to Forsting et al. relates to an energy absorbing band anchored on the door end walls. U.S. Pat. No. 4,328,642, relates to a stamped intrusion beam attached to the inner door frame of a vehicle.
None of the above-discussed devices is without its problems. While these known devices may have proven satisfactory for applications in the past, their efficiency, cost, methods of manufacture, and occupant protection capacity can be improved.